Silica refractory



United States Patent M 3,235,665 SILICA REFRACTORY Donald F. King, Pittsburgh, Pa, assignor to Harbison- Walker Refractories Company, Pittsburgh, Pa, a corporation of Pennsylvania No Drawing. Filed Jan. 16, 1964, Ser. No. 337,996 6 Claims. ((Ii. 106-69) The present invention relates to improved silica refractory shapes and brick and, in particular, to impregnated silica shapes for use in glass tank furnaces.

Silica refractories are used extensively in the metallurgical industries on account of their desirable properties, particularly their high melting point and their rig- 3,236,665 Patented Feb. 22, 1966 There is also typically present alumina in the amount of 0.6% or less, titania in an amount of 0.5% or less and alkalies in an amount of 0.5% or less. The balance of the brick consists of silica rock which may be in the form of quartzite or silica rock. See, for example, the US. patent to Harvey et al., 2,351,204, for a preferred silica brick. The fired brick is impregnated throughout its interstices with a high purity aqueous colloidal silica.

The colloidal silica impregnant employed in the present invention typically contains from about to 50% of SiO based on a total solids content. The colloidal silica may also contain up to a 1% maximum of a stabilizer, such as, ammonia and sodium; however, an ammonia stabilizer is preferable since it volatizes at eleidity and strength at high temperatures. For instance, 15 vated temperatures. Other volatile stabilizers, of course, they are used in the construction of roofs of open hearth may be employed without departing from the spirit of steel furnaces, which represent perhaps the most severe the invention. Also, the colloidal silica employed herein operating conditions to which these refractories are exhas a pH of from about 3.5 to 10.5; however, the pH posed. Silica refractories are also used extensively in the of many of the colloidal silica solutions employed have glass industry for lining the crowns and other parts of been found to fall between 8 and 10. Such colloidal the glass tank furnaces. These refractories are desirable silica are commercially available items of commerce. in this latter environment owing to their ability to with- Table I below lists several of the colloidal silica emulstand the corrosive atmosphere prevailing in glass meltsions suggested for use in the present invention. The ing furnaces. It is highly desirable in the applications silica refractory shapes are conveniently prepared by above mentioned that the silica brick be of relatively high making a batch by crushing and thoroughly blending density and strength and relatively low porosity. the components and mixing with a tempering and/or Silica brick are commonly made from quartzite or bonding agent.

TABLE I A B o D E F G H I J K L M thesis 2b) pI-llat25C 9.5 9.8 8.4 8.5 86 102 8.0 3,7 3.7 99 9a 99 93 Average Particle size (mu) 15 15 15 7 8 l3 19 19 19 37 17 37 17 silica rock to which a bonding agent, such as, the oxides The batch is compressed into brick on a brick press of calcium, megnesium, strontium, manganese, zinc, at a pressure of from about 2000 to 8000 p.s.i. The nickel, cobalt, and iron, is added. Typical practice is to 40 green brick are dried and then fired in a kiln at a temcrush and grind the rock to provide a suitable proportion perature of from 2300 to 2700 F. The fired brick are of coarse and fine grain sizes. The sized rock is then cooled and impregnated with colloidal silica by immersmixed with one of the binders mentioned, and water, and ing them in a vessel containing the colloidal silica bath refractory shapes are made from the mixed batch as by for about one-half hour. The vessel may be evacuated power pressing, impact pressing, or hand molding procor subjected to pressure or both to facilitate impregnaesses in accordance with standard techniques developed tion, in the roduction of silica refractories. A plurality of silica brick were prepared having the It is an object of the present invention to provide composition disclosed in US. Patent 2,351,204, by Harsilica brick with increased density and strength and devcy et al. The components were crushed and blended tocreased porosity than is presently experienced. 5O gether to give a typical brickmaking grind as follows:

Other objects of the invention will become apparent percem hereinafter. 6+l0 Tyler mesh 10 We have discovered, and it is upon this that our inven- -10441 30 tion is in large part predicated, tha by impregna ing -28-|-65 15 fi ed silica brick with high purity, aqueous colloidal 65 45 silica, the brick has enhanced strength and improved About 5%, by Weight of Water was added as a temper dgnslty very appreciable reduction porosity ing agent. The batch was then pressed into a plurality without impairlng the refractormess of sa d brlck. of brick measuring 9X 41/2 at about 4000 psi The glass in dustrles have found, that silica brick, after The brick were removed from the press, dried and fired extended use in the crowns of the glass tank furnaces, at a temperature of about 25500 R The brick were become m W a 1 a refefred to m the placed in a vessel and immersed in a colloidal silica susas mdymlte fuzz Y dfiletenmhs to glass ension as indicated in the tables following. The immanufacture- We have dlscovered that by f pregnant is indicated by a letter with reference to Table I. ing the silica brick with colloidal silica, the formation of In the pmferred embodiment, a vessel is evacuated tridymite fuZZ is Bfiactively curtailedto about 700 millimeters of Hg until no bubbles can be Briefly, in accordance With the Present invention, there observed leaving the brick. The vacuum is then broken is Provided a Silica refractory brick formed from a and the samples are removed from the solution and dried. bat h C s s g y g from about 1 t0 Brick made in this manner were tested for density, of one or more of the oxides of calcium, magnesium, 7O porosity, and modulus of rupture and the results are in- .strontium, manganese, zinc, nickel, cobalt and iron.

dicated below in Table II.

TABLE II Irupregnant None G H Density (p.c.i.) 114 120 123 Porosity (pereent) 22 17.8 15.2 Modulus of Rupture (p. 720 980 1,200

TABLE III Impregnant A None Density (p.c.f.) 117 106 Porosity (percent) 16.7 26.3 Modulus of Rupture (p.s.i.) 1,130 690 Here. also, the results indicate an appreciable increase in density and modulus of rupture and a decrease in porosity of the impregnated as compared with the nonimpregnated brick.

Several similar brick samples were tested to determine the effect of more than one impregnation treatment. The brick were tested to determine the permeability (which is a good indication of relative porosity) and the results are tabulated below in Table IV.

TABLE IV lmpregnaut G I G I None Number of Treatments 3 1 Permeability, K 1 0.0 0. 24 0. 96

1 K=cu. in. gas per sq. in. of area, sec. of time and lbs. pressure per in. of thickness.

The results indicate that a single impregnation treatment with the G impregnant showed a marked decrease in permeability, and thus porosity, as compared with the untreated brick. Further, the results indicate an additional decrease in porosity and permeability for the brick impregnated in 3 treatments.

It is apparent from the foregoing that fired silica refractory brick impregnated with a high purity, aqueous colloidal silica, had superior properties as compared with the same silica brick without impregnation.

It should be understood that other silica brick compositions, such as, those classified under ASTM Designation C 41660, may be impregnated in accordance with this invention.

Colloidal silica and phosphoric acid have been employed to impregnate graphite shapes to improve the oxidation resistance thereof (US. Patent 2,897,102). Colloidal silica has also been employed in combination with cement to impregnate porous concrete (see US. Patent No. 2,434,301).

While the invention has been described with reference to particular embodiments and examples, it will be understood, of course, that modifications, substitutions and the like may be made therein without departing from its scope.

I claim:

1. As a glass tank furnace lining, fired silica refractory brick comprising from about 1 to 5% of at least one oxide of the group consisting of oxides of calcium, magnesium, strontium, manganese, zinc, nickel, cobalt and iron, the balance silica rock, and impregnated throughout its interstices with a high purity, aqueous, colloidal silica, said colloidal silica containing from about 15 to 50%, by weight, SiO on an oxide basis, and up to 1% maximum of a stabilizer.

2. A fired silica refractory brick suitable for use in a glass tank furnace formed from a batch consisting of, by weight, from about 1 to 5% of at least one oxide of the group consisting of oxides of calcium, magnesium, strontium, manganese, zinc, nickel, cobalt and iron, the balance silica rock, and impregnated throughout its interstices with a high purity, aqueous, colloidal silica, said colloidal silica containing from about 15 to 50%, by weight, SiO on an oxide basis, and up to 1% maximum of a stabilizer.

3. The product of claim 2 in which the stabilizer is selected from the group consisting of ammonia and Nazo.

4. A fired silica refractory brick suitable for use in a glass tank furnace formed from a batch consisting of, by weight, from about 1 to 5% of at least one oxide of the group consisting of oxides of calcium, magnesium, st'rontium, manganese, zinc, nickel, cobalt and iron and the balance silica rock and impregnated throughout its interstices with a high purity, aqueous, colloidal silica containing about 30%, by weight, of SiO on an oxide basis, and about 0.26% of NH 5. A method for producing a silica refractory brick comprising disposing a batch consisting of, by weight, from about 1 to 5% of at least one oxide of the group consisting of oxides of calcium, magnesium, strontium, manganese, zinc, nickel, cobalt and iron and the balance silica rock, in a mold, compressing the batch at a pressure of from 2000 to 8000 p.s.i., firing the shape at a temperature of from 2300 to 2700 F., and immersing the shape in a bath of high purity, aqueous colloidal silica for a period of time sufiicient to impregnate throughout interstices in said shape.

6. A method for producing a silica refractory brick comprising a batch consisting of, by weight, from about 1 to 5% of at least one oxide of the group consisting of oxides of calcium, magnesium, strontium, manganese, zinc, nickel, cobalt and iron and the balance silica rock, in a mold, compressing the batch at about 4000 p.s.i., firing the shape at about 2550 F. and immersing the shape in a bath of high purity, aqueous colloidal silica for a period of time sufiicient to impregnate throughout interstices in said shape, said colloidal silica containing about 30%, by weight, SiO on an oxide basis, and 0.26% of NH References Cited by the Examiner UNITED STATES PATENTS 6/1944 Harvey et al. 106-69 4/1965 Smith-Johannsen 10669 

1. AS A GLASS TANK FURNACE LINING, FIRED SILICA REFRACTORY BRICK COMPRISING FROM ABOUT 1 TO 5% OF AT LEAST ONE OXIDE OF THE GROUP CONSISTING OF OXIDES OF CALCIUM, MAGNESIUM, STRONTIUM, MANGANESE, ZINC, NICKEL, COBALT AND IRON, THE BALANCE SILICA ROCK, AND IMPREGNATED THROUGHOUT ITS INTERSTICES WITH A HIGH PURITY, AQUEOUS, COLLOIDAL SILICA, SAID COLLODIAL SILICA CONTAINING FROM ABOUT 15 TO 50%, BY WEIGHT, SIO2, ON AN OXIDE BASIS, AND UP TO 1% MAXIMUM OF A STABILIZER. 